In devices using image sensor arrays, reduced resolution images are often output for purposes of image preview. For example, view finders in digital cameras often display a reduced resolution motion video image to illustrate a preview of a captured image. This may be followed by a full resolution capture when a user presses a capture button on the camera, or on a touch screen display. This functionality may also be found in cell phone cameras and other mobile devices using such image sensors.
There are certain attributes for a preview mode that may be beneficial. For example, a higher scan rate may be desirable to provide motion artifact clean video. Also, a relatively high signal to noise ratio (SNR) may be advantageous, because preview video is real-time, and often does not have the benefit of post-capture image processing to remove noise, increase gain, and so on. However, these issues can present a strain on power supply. Also, unlike a typical image capture, the camera may be in preview mode for long periods of time, and a series of images may be shown in succession. The recurring scans, and ongoing display of images, can also put significant strains on power. Because of the finite power supply often associated with digital cameras, cell phones, and other mobile devices with integrated cameras, these power consumption issues can be very limiting.
There are additional challenges as well, as although higher SNR may be achieved with long exposure time, this may come at the cost of lower scan rate. High quality preview may be achieved by filter-based downscaling of the image, but that may imply high power consumption. Low power consumption reduced resolution scan can be achieved with sub-sampled scan, but this may impact the SNR, as light accumulated in the non-scanned pixels may be lost.
Binning, wherein groups of same color neighboring pixels (for example, squares of 2×2 same color pixels) are accumulated right after the scan, may be used in certain circumstances to reduce power consumption. While this method may not have the benefit of a higher scan rate when the image is scanned at full resolution, reasonable SNR pictures may be achieved using simple low power consumption circuits for the addition of neighboring pixel values.
In light of this range of issues, it is desirable to identify methods and devices for providing reduced resolution video at adequate frame rates and SNR, while limiting power consumption.